Conventionally, as a control system for a vehicle, one disclosed in Patent Literature 1 is known. This vehicle includes a battery as a power source, a car audio device to which electric power is supplied from the battery, an ignition switch for starting an engine, and so forth. In this control system, when a power source position of the ignition switch is switched from an ignition position to an accessory position by a driver, an output of the car audio device is controlled such that it is reduced by a predetermined level so as to suppress reduction of the remaining charge capacity of the battery.